Phytoplankton taxa composition of the Caspian Sea were evaluated by using samples collected at 12 stations along the Iranian coast of the Caspian Sea between 1996 and 2010. This study identified 158 phytoplankton species consisted of diatoms (70 species), dinoflagellates (23 species), chlorophytes (29 species), cyanophytes (31 species), and euglenoids (5 species). The dominant species were the diatoms Thalassionema nitzschioides, Dactyliosolen fragilissimus, the dinoflagellate Prorocentrum cordatum, and the cyanophyte of genus Oscillatoria. The average species diversity index of phytoplankton community was 1.88 as recorded in this study. There were main changes in phytoplankton composition as compared with previous study. It could be related to the severe human activities and difference in sampling strategies
